The merozoite interacts in a receptor specific manner with the erythrocyte surface and is the stage against which immunity may work to block invasion. Thus, merozoite surface components are of interest for their role in erythrocyte recognition and as antigens for induction of protective immunity. We are now studying the processing of these molecules during the ultimate stages of parasite development, their role in reception and as immunogens for induction of protective immunity. The major glycoprotein of the P. falciparum has also been shown to be localized to the schizont surface and not on the erythrocyte. The Duffy blood group determinant involved in junction formation with P. knowlesi and P. vivax has been identified.